1. Field of the Invention
The present invention relates to a composition for preparing inorganic light weight foam, and a process of preparing inorganic light weight foam.
2. Description of the Related Art
Processes of manufacturing a rigid and light weight foam made by adding a foaming agent to a composition whose main components are a vinyl chloride-based resin and inorganic powder are disclosed in, e.g., Japanese Patent Publication No. 53-7944 and Japanese Patent Publication No. 52-26776. It is specified in these publications that the foaming agent used in these processes is liquid butane, and that the vinyl chloride-based resin used is a paste resin.
Besides these processes wherein an organic or inorganic foaming agent is used, other processes are known. In the process which is disclosed in Japanese Patent Disclosure No. 56-129236, a nitrile compound is added. In the process disclosed in Japanese Patent Disclosure No. 59-8660, an azo-based or sulfur-based free radical initiator is added. In the process disclosed in Japanese Patent Disclosure No. 61-151073, an organic peroxide is added.
According to the publications which disclose the processes wherein an azo-based or sulfur-based, free-radical initiator and an organic peroxide free radical initiator are added, radicals are generated by virtue of the heat generated when the inorganic powder and the vinyl chloride-based resin are kneaded together. These radicals induce no cross-linking of the vinyl chloride-based resin. Rather, the radicals induce the hydrogen abstraction of both the inorganic powder and the vinyl chloride-based resin, and also couple the fragments of the free radical initiator, thereby increasing the compatibility of both compounds (or activating both compounds) and promoting the homogeneous dispersion of these compounds.
In the known processes described above, a foaming agent and other additives are added to a composition whose main components are vinyl chloride-based resin and inorganic powder, thereby preparing a foamed body of a high expansion ratio. However, each is a process wherein all materials are merely mixed and dispersed, and the resultant mixture is foamed by means of a foam molding machine such as a press machine. This process does not use the step of "livering" (The term "livering" means a phenomenon wherein the resin comes into a molten state, as will be later described.) at an appropriate temperature under shearing force, until the step of charging the mixture into a mold of the foam molding machine. From a technical point of view, in the known processes, the vinyl chloride-based resin must be used in the form of a paste resin which resin is of very fine particle size such as less than several microns, as is specified in any patent publication or disclosure identified above.
As far as the present inventor knows, there is only one prior art publication, i.e., Japanese Patent Disclosure No. 63-85071, which teaches that conditions for shearing action and displacement action are technical points of vital importance.
In the process disclosed in Japanese Patent Disclosure No. 63-85071 a foaming agent and an organic peroxide or an azo compound having a specific activation energy is added to a composition whose main components are an inorganic filler and vinyl chloride-based resin prepared by suspension polymerization, mass polymerization, or emulsion polymerization, thereby to cross-link and foam the composition. The addition of the foaming agent and the organic peroxide or azo compound to the composition is carried out while the composition is undergoing particle dispersion and melt dispersion in a kneader which can perform shearing and displacement. It is true that this process has the same object as the present invention, that is, the prevention of leakage of foaming gas. Nonetheless, this is a process for preventing a leakage of foaming gas by means of the cross-linking of the composition, and the important actual means employed in this process are basically different from those used in the process according to the present invention.